Many integrated circuits (“ICs”) are made up of millions of interconnected devices, such as transistors, resistors, capacitors, and diodes, on a single chip of semiconductor substrate. It is generally desirable that ICs operate as fast as possible, and consume as little power as possible. Semiconductor ICs often include one or more types of memory, such as CMOS memory, antifuse memory, and e-fuse memory.
E-fuses are usually integrated into semiconductor ICs by using a stripe (commonly also called a “link”) of conducting material (metal, poly-silicon, etc.) between two pads, generally referred to as anode and cathode, so that at a fuse current level (IFUSE) the link is thermally destroyed, thus changing the resistance of the E-fuse. This is commonly referred to as “programming” the e-fuse. The fuse state (i.e., whether it has been programmed) can be read using a sensing circuit, which are common in the art of electronic memories.
Unfortunately, conventional E-fuses require substantial current to program, which can cause programming damage to other portions of the IC. Programming reliability is also a concern for conventional E-fuses. Manufacturing variations lead to variations in the optimal programming energy. In some instances, the link is not completely broken, or damage from fuse programming results in a current path having a resistance less than the resistance specified to indicate a programmed fuse.
Another problem arising with E-fuses is that conventional designs do not reliably scale to smaller design geometries. For example, an E-fuse that works acceptably well (i.e., reliably programs to a high-resistance state) in an IC fabricated according to a 90 nm node geometry might produce an unacceptably high number of programming failures when the IC is adapted to a smaller process node such as 65 nm node geometry. Similarly, smaller node geometries are often associated with a lower IC operating voltage, which provides less programming energy for a given programming current. Conventional E-fuses require programming conditions that may be difficult to obtain with a low-voltage IC.
It is desirable to provide E-fuses that avoid limitations of conventional E-fuses.